I'm not sure I understand your question, but I will try.
>>Why do you need to have 600W to power a graphics card?
You don't. There is no GPU currently that needs that much. But as cards are comfortably approaching 400W and more, a new connector is necessary so you don't end up with GPUs taking 3 or 4 existing PCIe 8-pin power connectors. This single 55-amp compatible connector allows for significantly easier routing of paths on circuit boards.
>>Why do they need an independent power connector?
Because the PCIe slot alone can only provide 75W of power. And if it could provide more you'd need to provide that power to the motherboard so you just moved your connector from one place to another.
>>Why do you need to have 600W to power a graphics card?
You don't. There is no GPU currently that needs that much. But as cards are comfortably approaching 400W and more, a new connector is necessary so you don't end up with GPUs taking 3 or 4 existing PCIe 8-pin power connectors. This single 55-amp compatible connector allows for significantly easier routing of paths on circuit boards.
>>Why do they need an independent power connector?
Because the PCIe slot alone can only provide 75W of power. And if it could provide more you'd need to provide that power to the motherboard so you just moved your connector from one place to another.